1. Field of the Invention
This invention relates to a control system for controlling a device which is adapted to coat a body with a wear layer and which comprises a frame on which the body can be rotatably arranged, a system for producing a mass of elastomeric material, a system for discharging the mass of elastomeric material and forming it into a strand, a system for applying the strand on the body so as to form the wear layer, and a system for automatic feedback control of the coating of said body.
Coating a body, such as a tire carcass or a roller in a papermaking machine, with elastomeric material, such as rubber, in the form of strands (which are subsequently vulcanized), is not without its problems. Hitherto, it has not been possible to solve these problems in a satisfactory fashion. The present application concerns a technique for coating a hotly with rubber that aims at providing the rubber layer or tread with a certain profile, i.e. a certain outline and/or thickness. The profile is dependent on the dimensions of the rubber strand applied and on the closeness of the turns of rubber strand, which generally is identical with the degree of overlapping between one turn and the immediately preceding turn.
2. Related Background Art
There exist today control systems and methods aiming at achieving a certain, desired profile. In a prior-art method, the system controlling the coating machine is supplied with predetermined values of the closeness of the turns, and the machine i.. then operated according to these values with the aid of the control system, a predetermined rubber thickness being approximately achieved at each point on the body.
In another prior-art method, a template for the final profile is arranged behind the body, and an operator controls, via the control system, the coating with rubber while watching the body and the template in order to ensure that a profile corresponding to the template is obtained.
There are many problems associated with the above prior-art methods, and these problems are due to the control system itself as well as the way this is used. These problems are long standing, and the best efforts to find a solution have resulted in the control systems described above.
Thus, the scrap percentage is embarrassingly high, and the quality of the end product leaves much to be desired, especially in certain applications, such as retreading and other sorts of recapping where the body is not new but merely reconditioned in view of the coating process.
Additionally, in the prior art, the rubber consumption is far from optimal. In mass production of the type commonly used in this field, each saved gram of rubber is important, at least from the economic point of view, and there is thus a great demand for a technique enabling a minimization of the rubber consumption.
These problems are primarily due to very approximate and inaccurate control of the rubber coating itself, the variations in a body or the variations between bodies of the same type being not taken into consideration, as in the first-mentioned prior-art technique, and/or the errors being overcompensated, as in both prior-art techniques described above. Consequently, an uneven body may result in an uneven rubber layer. Excessive amounts of rubber are applied to ensure that an aimed-at minimum thickness is achieved. Furthermore, the method using visual inspection for comparing the rubber layer with a template also involves an excessive rubber consumption, owing to the operators inability to assess the results correctly, for which reason the rubber layer will be thicker than is strictly necessary to ensure that the template is covered.
Furthermore, there does not exist any efficient and cost-effective method for checking the quality of the body, which may vary within wide limits, primarily in certain applications, such as retreading. In combination with the above-mentioned control problems, this means that an unintentional irregularity of the body, such as an oval or crooked shape, affects also the rubber layer, resulting in an end product of irregular shape, which too often has to be scrapped. This leads to excessive production costs, a waste of raw material and energy, as well as complaints from customers, and may even result in a dangerous end product which, in the worse case, may pass the final inspection. In the second-mentioned prior-art technique, it is true that some irregularities may be compensated for, but also here are some irregularities, such as an oval shape as well as local irregularities not found in a whole turn, transferred to the rubber layer. When a portion of the body has a smaller or larger diameter than is assumed in the process, there is, furthermore, a risk that the rubber layer applied, which gives a profile approximately agreeing with the template, will be thicker or thinner in this portion than is deemed suitable.